Interpretive Summary: Rice kernels contain close to 90% starch, and the starch is responsible for how rice ingredients perform in food systems. In the processing of rice ingredients, treatments with various heat and moisture conditions are normally involved, which could alter the food-use properties of the products. In this study, we treated rice starches from waxy and long grain rice cultivars with two sets of modification procedures. One is called annealing (ANN) that is done in excess water, low temperature (50 C), for 24 hours. Another one is called heat-moisture treatment (HMT) that is done in relatively low water contents (20 to 40%), high temperature (110 C), for 8 hours. The study provides an insight on changes in the crystalline structure of the starch during these treatments. Also, it was found that both ANN and HMT improved the pasting and gelling stability of the starch, more so with HMT. The information enhances our basic understanding on the chemistry that is involved in starch processing, and is useful for the food industry in food product development using rice ingredients.

Technical Abstract:
Rice starches of long grain and waxy cultivars were annealed (ANN) in excess water at 50 oC for 4 hours. They were also modified under heat-moisture treatment (MHT) conditions at 110 oC, and various moisture contents (20%, 30%, and 40%) for 8 hours. The modified products were analyzed by Rapid-Visco Analysis (RVA), Differential Scanning Colorimetry (DSC), and X-ray Diffraction (XRD). Generally, these hydrothermal treatments altered the pasting and gelling properties of rice starch resulting in lower viscosity peak heights, lower setbacks, and greater gelling stability. The modified starch showed increased gelatinization temperatures, and reduced peak widths, or gelatinization temperature ranges on ANN or broader ones on HMT. The effects were more pronounced for the HMT than ANN. Also, the typical A-type XRD pattern for rice starch remained unchanged after ANN or HMT at low moisture contents, and it changed to an amorphous form after HMT at >30% moisture contents.